This invention relates generally to an apparatus and method for inserting an insulation sheet into the slots of a stator core. More particularly, this invention relates to an apparatus and method for inserting an insulation sheet used for insulating multi-phase coils from each other, which coils are wound around a stator core of an electric rotary device such as an electric motor, into the slots of a stator core.
Generally, there are two methods of insulating stator coils. One of these methods is "slot insulation," in which insulation sheets are placed in the slots of the stator core. In this method the insulating sheet insulates the inside surface of the slots from the coil wires in the slots. In the second method, "phase insulation," insulation sheets are partially inserted into certain slots of the stator core to insulate the coil of a first phase from that of a second phase. A number of slot insulation devices have been developed. These devices automatically insert insulation sheets into the slots simultaneously with insertion of coil wires into the same slots. These devices are used effectively in automated wire-inserting processes.
In contrast, phase insulation has typically been carried out manually. Automation of the phase insulation process has proven difficult because the phase insulation process requires manipulating a very thin insulation sheet, having a pair of parallel strap portions interconnected by a pair of connecting portions, and, particularly, because it requires that the insulation sheet be bent into an arcuate shape. To compound the problem, the connecting portions must be inserted into two designated slots to achieve proper positioning of the sheet. Because this process is carried out manually, it requires a great deal of worker attention and results in a loss of worker productivity.
Japanese patent Kokoku No. 59-39982 describes a phase insulation device which can solve the previously described problem. This device is illustrated in FIGS. 8 and 9. In FIG. 8, an insulation sheet 101 is held in an upright position on a forming block 102 by a vacuum. The forming block 102 is moved in the direction of the arrow "Q", from the position shown in FIG. 8, and sandwiches the sheet 101 between itself and upper and lower blocks 103 and 104. This action corrugates the sheet 101. A center clamp 105 is lowered to temporarily secure the sheet 101 to the upper and lower blocks 103 and 104.
Meanwhile, a piston 106, as shown in FIG. 9, is activated to secure the opposite end portions of the sheet 101 to the positions between an upper side clamp 107 and the upper block 103 and between a lower side clamp 108 and the lower block 104. Subsequently, the forming block 102 is moved back to its initial position and the connecting portions 101a of the sheet 101 are placed into grooves 109a of pusher guides 109, respectively.
A stator 110 is positioned above the upper block 103 and the stator 110 is lowered after the slots 111 are aligned with the pusher guides 109, as shown in FIG. 9. Then, pistons 113 in a tooling 112, as shown in FIG. 8, are extended until the pusher guides 109 abut the inside surface of the stator 110. This causes the sheet 101 to become stationary while the connecting portions 101a are brought into alignment with the respective slots 111 of the stator 110. Next, the center clamp 102 and the upper and lower side clamps 107 and 108 are loosened to release the sheet 101. Once the sheet 101 is released, pistons 114 in the tooling 112 are extended and move pushers 115 through the pusher guides 109 toward the stator 110 to insert the connecting portions 101a into the respective slots 111 through the slot openings 111a. After this step, the sheet 101 expands due to its own resiliency to conform to the inside diameter portion of the stator 110 and the insertion process of the insulation sheet 101 is completed.
The previously described conventional insertion process is relatively uncomplicated because each of the connection portions 101a of the insulation sheet 101 consists of one leg or strip. However, the connecting portions 101a inserted by this conventional process tend to disengage from their respective slots when the strap portions of the sheet 101 are subject to an external force, such as a tensile force.
A new type of insulation sheet, which can be used to solve the above described problem, is available. The sheet is typically struck from an insulating sheet material. This new insulation sheet has a one-piece construction in which the connecting portions and the body portions are integrally formed with each other. The width of each connecting portion is greater than that of the opening of the associated slot. Each connecting portion is divided into two strips by a slit running lengthwise between the strips. Thus, the connecting portions have four total connection strips. These four connection strips are each inserted into separate slots of a stator core to inhibit accidental disengagement of the connection portions from the slots. However, automating the insertion process for this new sheet is also very difficult and no apparatus for carrying out such a process has previously been commercially available.